Transparent ceramics have been successfully used in a variety of applications such as scintillator media in radiation detectors and computer tomography screens, gain media in solid state lasers, and strike faces of transparent armor systems for personnel protection from both military and civilian threats.
The principal hurdle in the processing of transparent ceramics is that current approaches are limited to the relatively few possible materials with thermodynamically stable cubic crystal structures. The class of materials from the rare earth aluminum and rare earth gallium garnets requires particularly narrow compositional ranges to result in single phase ceramics. Cubic crystal structures are required in order for optical scatter to be low enough to result in transparency. So far, transparent ceramics from non-cubic crystal structures have required either very small grain sizes (nanometer-scale) or very large grain sizes (millimeter-scale), where scatter arising from the birefringence of non-cubic phases is minimized. These fabrication regimes are not typical for ceramics processing; in fact, grain sizes in the 1-10 micron range are more typical, and require cubic crystal structures in order to achieve acceptable optical transparency.
Researchers in the area of transparent ceramics were previously only able to work in the limited number of rare-earth aluminum and gallium garnet compositions that are thermodynamically stable from the processing temperature to operation temperature. To satisfy the very narrow range of chemical compositions processors of starting materials for transparent ceramics have relied on extremely accurate analyses of the metal contents of the chemical precursors or have retreated to an iterative approach of varying the composition of the chemical precursors, processing the powders to dense ceramics, examining the finished ceramics for secondary phases, and altering the starting composition to compensate for compositional error.